Senior politicians and HM Revenue & Customs have been accused of failing to act over claims that HSBC helped clients dodge millions of pounds in taxes.
A furious blame game is under way between the Tories and Labour after a huge trove of files on secret Swiss accounts run by the bank were leaked.
The documents have already sparked criminal probes in several countries and attempts to claw back cash after being stolen by an IT worker in 2007 and passed to French authorities.
Now the details of 30,000 accounts holding almost £78 billion of assets are being revealed after they were obtained by a French newspaper and analysed by a team of investigative journalists.
They are reported - by BBC's Panorama and the Guardian - to include evidence that the bank colluded with some clients to hide accounts from tax authorities in their home countries.
Holding a secret bank account is not illegal but they have been used by some to deliberately conceal assets in order to dodge tax, which is against the law.
The BBC said the documents include details of almost 7,000 British clients.
HMRC, which was passed the data in 2010, has clawed back £135 million from some of the 3,600 Britons identified as potentially avoiding tax using the Geneva branch of HSBC.
Only one prosecution has been brought.
Public Accounts Committee (PAC) chair Margaret Hodge said Lord Green, who ran HSBC during the period and was appointed trade minister in 2010, faced "serious questions". The peer stepped down from the Government post at the end of 2013.
"Either he didn't know and he was asleep at the wheel, or he did know and he was therefore involved in dodgy tax practices," the Labour MP told BBC Radio 4's Today programme.
"Either way he was the man in charge and I think he has got really important questions to answer."
Mrs Hodge said HMRC had not been sufficiently determined in tackling dodgy practices. "You are left wondering, as you see the enormity of what has been going on, what it actually takes to bring a tax cheat to court," she told BBC Radio 4's Today programme.
"If it had been a benefit cheat it would have been up for court years ago. Now we have had only one tax cheat taken before the British courts."
Mrs Hodge said countries such as the US, France and Argentina were taking action against HSBC over its activities. "We are never assertive enough, aggressive enough and I think just determined enough to actually protect the taxpayer," she said.
"It makes me really frustrated that we have our tax authorities facing both ways. On the one hand, they are all part of the establishment, we want to look after them, on the other hand not defending really the taxpayer's interest."
City Minister David Gauke insisted he "was not aware of any evidence" that Lord Green had been involved in any of the activity.
"Clearly HSBC have got questions to answer," he told Today. "In terms of Stephen Green, I don't think there is any suggestion or any evidence that he was involved or engaged in some of the behaviour that occurred in the subsidiary in Switzerland.
"The regulators have not found that was the case. Indeed I think there is a view that Stephen Green was to some extent clearing up a mess."
Mr Gauke said the system was now far stronger - and pointed out that shadow chancellor Ed Balls had been in the Treasury when behaviour was at its worst.
"I do have to make the point that there was a lack of grip in this area and a lack of progress in dealing with tax cheats," he told BBC Breakfast.
"In particular that era, 2005-2007, tax avoidance schemes were prevalent, it was very common for people to hide assets off shore.
"I think there are questions to be answered by the likes of Ed Balls, who was City Minister at the time, what was he doing to deal with this type of behaviour and tax evasion by British residents?"
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